The present invention relates to a flexible tube for an endoscope which is used for medical care, and a method of manufacturing the flexible tube for an endoscope.
Up to now, a flexible tube for an endoscope, which is inserted into a living body such as a human body and used for diagnosis and treatment of organs, extraction of samples, and the like, includes a spiral tube (flex) in which a thin band-shaped plate is wound spirally, a braid (net) covering an outer circumferential surface of the spiral tube, and a resin outer skin covering an outer circumferential surface of the braid.
In the conventional flexible tube for an endoscope having the structure as described above, the braid is provided between the spiral tube and the outer skin and bonded to an inner circumferential surface of the outer skin to serve as a rigidity reinforcing material of the flexible tube. In other words, unlike a case where the spiral tube is covered with only the outer skin, the braid reinforces the rigidity of the flexible tube.
The braid as described above is normally formed by knitting metal fibers such as stainless steel fibers or brass fibers. Therefore, for example, when a general resin outer skin is formed on the outer circumferential surface of the braid by a general formation method such as extrusion molding, there are many cases where the bonding (contact or joining) strength between the braid and the outer skin of the flexible tube is reduced during the use of the endoscope because chemical bonding between metal and a resin is basically only weak bonding with intermolecular forces.
The chemical bonding between metal and a resin is vulnerable to water. Therefore, when the endoscope is used under the presence of moisture such as water or steam or when the endoscope is frequently cleaned with water, a disinfection solution, a cleaning solution, or the like, the bonding strength between the braid and the outer skin of the flexible tube is quickly reduced.
When the bonding strength between the braid and the outer skin is reduced in the flexible tube for an endoscope as described above, the function of the braid serving as the rigidity reinforcing material of the flexible tube deteriorates to reduce the rigidity of the flexible tube, with the result that the use of the endoscope is adversely affected in many cases. In addition, when the bonding strength between the braid and the outer skin is reduced in the flexible tube, the braid and the outer skin may be peeled off from each other to buckle the flexible tube, thereby disabling the use of the endoscope.
To address this problem, JP 59-137030 A discloses a flexible tube for an endoscope, in which a net-tube-shaped braid formed by knitting a fiber material is bonded (joined) to an outer skin (outer tube) by a cohesive agent.
JP 61-256085 A discloses a flexible tube for an endoscope, in which fibers made of a thermoplastic resin are intervolved with at least one metal wire of a metal wire group composing a braid and melted to bond the braid to an outer skin.
JP 61-046923 A discloses a flexible tube for an endoscope, in which a release agent is interposed between the spiral tube (flex) and the braid, and the braid and an outer skin made of a synthetic resin are bonded (jointed) to each other by a polyester-based urethane bonding material which is applied on the surface of the braid and contains toluene diisocyanate as a monomer.
In the flexible tube for an endoscope disclosed in JP 59-137030 A, the braid and the outer skin are bonded to each other by the cohesive agent. Therefore, while the flexible tube is prevented from hardening that occurs when the bonding material is used, the braid and the outer skin of the flexible tube can be prevented from being peeled off from each other, that is, the bonding strength can be prevented from reducing. However, the cohesive agent is generally made of a resin and thus the bonding thereof to metal is weak, and hence the reduction in bonding strength between the braid and the outer skin is not substantially different from that in conventional flexible tubes for an endoscope.
In the flexible tube for an endoscope disclosed in JP 61-256085 A, a part of the braid is the fibers made of a thermoplastic resin, and hence the braid is connected to the fibers serving as bonding materials by physical force. When the fibers are melted, the braid and the outer skin are bonded to each other, and hence the bonding strength (contact strength or joining strength) between the braid and the outer skin may be higher than that in the flexible tube in which the braid and the outer skin are bonded to each other by only the bonding material. However, as the flexible tube, that is, the endoscope is used over time, the bonding strength between the braid and the outer skin is reduced to lower the rigidity of the flexible tube.
In the flexible tube for an endoscope disclosed in JP 61-046923 A, the braid and the outer skin are bonded to each other by the polyester-based urethane bonding material containing the toluene diisocyanate as the monomer. Therefore, the bonding between the braid and the outer skin is stronger than that in a conventional flexible tube using a bonding material. However, the braid and the outer skin are bonded to each other fundamentally by the bonding material made of a resin. Thus, even though an endurance time is longer than that in the conventional flexible tube using the bonding material, the bonding strength between the braid and the outer skin is eventually reduced.